1. Field of the Invention
The present invention relates to a method and apparatus for aligning masks with semiconductor wafers.
2. Discussion of Related Art
Referring to FIG. 1, photolithography typically involves a substrate 101 covered with a photosensitive material or a resist that can be patterned. Patterns to be formed on the substrate 101 can be etched on a mask 102. The mask 102 can be used to transfer a pattern to the imageable photoresist layer of the substrate 101. Reduction optics 103 can be used to focus radiation from a light source 104 onto an area of the substrate 101.
Alignment of the mask 102 to the substrate 101 is important to manufacturing functional devices, and in particular to forming devices having small design rules, e.g., small critical dimensions. Alignment is the process of positioning the mask 102 over a predetermined position on the substrate 101, wherein the position can be determined relative to alignment marks. Alignment marks help ensure that the mask 102 can be aligned precisely with respect to the wafer 101.
Traditional alignment methods, wherein the alignment marks are located on a periphery of the chip, show limited performance for small ground rules. This is because, for example, the alignment marks in the periphery can be far away from the structure being patterned, wherein small deviations of the mask from the substrate can be exaggerated as the distance from the alignment mark increases.
Therefore, a need exists for a high-contrast, small alignment mark that can be implemented as means for an intra-cell alignment.
According to an embodiment of the present invention, a method for intra-cell alignment of a substrate and a mask comprises providing the substrate comprising a photosensitive material and an alignment structure in an intra-cell region of the substrate, providing a mask comprising a phase-shift region, and aligning the phase-shift region to the alignment structure of the substrate.
The method further comprises determining a phase conflict region, and determining the alignment structure of the substrate.
The method further comprises exposing a field of the substrate to actinic light to pattern the photosensitive material.
The alignment structure comprises a dot, a line, and/or a rectangle.
According to an embodiment of the present invention, a wafer comprises a first alignment structure positioned in a periphery of the chip, a plurality of cells formed on a surface of the wafer, and at least one second alignment structure formed between the plurality of cells.
According to an embodiment of the present invention, a method for intra-cell alignment of a substrate and a mask comprises providing the substrate comprising a photosensitive material, a first alignment structure in a periphery region of the substrate and a second alignment structure in an intra-cell region of the substrate. The method comprises providing a mask comprising a phase-shift region, pre-aligning the phase-shift region to the first alignment structure of the substrate, and aligning the phase-shift region to the second alignment structure of the substrate.
Pre-aligning comprises determining a phase conflict region, and determining the first alignment structure of the substrate.
The method comprises exposing a field of the substrate to actinic light to pattern the photosensitive material.
The second alignment structure comprises a dot, a line, and/or a rectangle.